Hydraulic systems include engines, hydraulic pumps, and hydraulic motors, and are used for consumer and commercial products, industrial processes, and systems for vehicles. One example of a hydraulic motor, used for example in the drive system of zero-turn-radius mowers, is a geroller motor. A geroller motor may be driven, for example, by a variable displacement piston pump to provide rotary motion for rotating a mower drive wheel.
Geroller motors typically have one of two types of shafts. A geroller motor having a flexible shaft that wobbles, such as a splined “dog-bone” shaft, typically has one moving member, such as an inner rotor, that both rotates and orbits with respect to a central longitudinal axis extending longitudinally through the geroller motor. Alternatively, a geroller motor having a straight-through shaft supported by bearings on both ends often includes two revolving members, an outer ring and an inner rotor. The outer ring is disposed about and interengages with the inner rotor. The members are received within a locating ring or casing. Movement of the members with respect to one another, and with respect to the casing, allows for full stationary contact between the shaft and the inner rotor. This contact allows the shaft to be extended through the hydraulic motor for mounting auxiliary devices, such as parking brakes, auxiliary drive functions, or encoders for speed readout or closed loop control.
Straight-through shaft geroller motors often operate at high temperatures and pressures where structural integrity is an important factor. The arrangement of the members and straight shaft allows for low internal pressure drop, high mechanical efficiency, high flow capability, and high torque output.